Unpaired Electron Research Articles

Electron and Spin Delocalization in [Co6 Se8 (PEt3 )6 ]0/+1 Superatoms.

Molecular clusters can function as nanoscale atoms/superatoms, assembling into superatomic solids, a new class of solid-state materials with designable properties through modifications on superatoms. To explore possibilities on diversifying building blocks, here we thoroughly studied one representative superatom, Co6 Se8 (PEt3 )6 . We probed its structural, electronic, and magnetic properties and revealed its detailed electronic structure as valence electrons delocalize over inorganic [Co6 Se8 ] core while ligands function as an insulated shell. 59 Co SSNMR measurements on the core and 31 P, 13 C on the ligands show that the neutral Co6 Se8 (PEt3 )6 is diamagnetic and symmetric, with all ligands magnetically equivalent. Quantum computations cross-validate NMR results and reveal degenerate delocalized HOMO orbitals, indicating aromaticity. Ligand substitution keeps the inorganic core nearly intact. After losing one electron, the unpaired electron in [Co6 Se8 (PEt3 )6 ]+1 is delocalized, causing paramagnetism and a delocalized electron spin. Notably, this feature of electron/spin delocalization over a large cluster is attractive for special single-electron devices.

Thermal conductivity suppression in uranium-doped thorium dioxide due to phonon-spin interactions

In this work, impact of low level of uranium (U) atom substitution on thermal conductivity of thorium dioxide (ThO2) is investigated. ThO2 is an electronic insulator with a wide optical band-gap and no unpaired electrons whose thermal transport is governed by phonons. U-substitution introduces unpaired f-electrons resulting in paramagnetic behavior of UThO2 at room temperature, which significantly suppresses its thermal conductivity. A single crystal of UThO2 with graded composition of U is grown using a hydrothermal synthesis method, and thermal conductivity measurements are performed in regions with uniform composition of U at levels of 0%, 6%, 9% and 16%. Measured thermal conductivity profiles over 77–300 K temperature range are analyzed using an analytical expression for phonon-mediated thermal transport based on Klemens-Callaway model. Temperature dependent thermal conductivity is found to deviate significantly from the Rayleigh scattering trend expected for a simple substitutional point defect with a small perturbation to mass and interatomic forces. With the resonant scattering term, observed large suppression of thermal conductivity at low temperatures can be closely reproduced. Additionally, the extracted phonon-spin coupling constants imply a nonlinear relation of phonon-spin interaction intensity with respect to U doping percentage. Our study reveals how phonon-spin scattering contributed by unpaired f-electrons in U atoms influences thermal transport in the UThO2 system.

Unraveling Synergistic Effect of Defects and Piezoelectric Field in Breakthrough Piezo-Photocatalytic N2 Reduction.

Piezo-photocatalysis is a frontier technology for converting mechanical and solar energies into crucial chemical substances and has emerged as a promising and sustainable strategy for N2 fixation. Here, for the first time, defects and piezoelectric field are synergized to achieve unprecedented piezo-photocatalytic nitrogen reduction reaction (NRR) activity and their collaborative catalytic mechanism is unraveled over BaTiO3 with tunable oxygen vacancies (OVs). The introduced OVs change the local dipole state to strengthen the piezoelectric polarization of BaTiO3 , resulting in a more efficient separation of photogenerated carrier. Ti3+ sites adjacent to OVs promote N2 chemisorption and activation through d-π back-donation with the help of the unpaired d-orbital electron. Furthermore, a piezoelectric polarization field could modulate the electronic structure of Ti3+ to facilitate the activation and dissociation of N2 , thereby substantially reducing the reaction barrier of the rate-limiting step. Benefitting from the synergistic reinforcement mechanism and optimized surface dynamics processes, an exceptional piezo-photocatalytic NH3 evolution rate of 106.7µmolg-1 h-1 is delivered by BaTiO3 with moderate OVs, far surpassing that of previously reported piezocatalysts/piezo-photocatalysts. New perspectives are provided here for the rational design of an efficient piezo-photocatalytic system for the NRR.

Determination of antioxidant activity, total phenolic and total flavonoid contents in tamarillo (Solanum betaceum) peel's ethanolic extracts

Background: Free radicals are chemical species a molecule, atom with unpaired electrons and reactive as oxidizing agent which cause oxidize stress in tissue. Antioxidants are substances that can protect cells from free radicals by releasing electrons to neutralize free radicals. Tamarillo peel contains phenolic and flavonoid compounds which have antioxidant activity. The aim of this study was to determine the antioxidant activity, total phenolic and flavonoid content of the ethanol extract of tamarillo peel. Methods: In this research, the maceration method was used to extract phenolic and flavonoid components from tamarillo peel with ethanol 70% solvent. Total phenolic and flavonoid content was determined with UV-vis spectrophotometer. Total phenolic content determined using the Folin-Ciocalteu reagent and expressed in GAE (Garlic acid equivalent) and the total flavonoid content used the AlCl-3 reagent and expressed in QE (Quersetin equivalent). Then, tamarillo peel ethanol extract was tested the antioxidant activity using the DPPH method. Result: The results showed that the total polyphenol content was 66.6242 mg GAE/g extract or 6.66% w/v extract, total flavonoid content was 0.74246 % w/v or 7.4246 mg QE/g extract. Antioxidant activity in IC50 value was 47.9460 ppm. Conclusions: From the results of the research conducted, it can be seen that the ethanol extract of tamarillo can provide an antioxidant effect in the very strong category.

Unexpected Reduction of a Coordinated Diazapyridinophane Ligand Bound to Chromium(III) Ion Leading to Delocalization of the Unpaired Electron across Two Isolated Pyridine Units.

In the tetraazamacrocyclic ligand N,N'-dimethyl-2,11-diaza-[3.3](2,6)pyridinophane (L-N4 Me2 ), the two pyridine units are separated from each other by sp3 -hybridized triatomic bridges. Such electronically isolated pyridine moieties are considerably less prone to reductions than di- or triimines. A detailed structural, magnetic, and spectroscopic investigation of the complexes [Cr(L-N4 Me2 )(OAc)2 ] and [Cr(L-N4 Me2 )(OAc)2 ](PF6 ), in combination with theoretical calculations, reveals that the reduced complex must be described as a chromium(III) ion coordinated to the anionic radical ligand (L-N4 Me2 )⋅- rather than a low-spin chromium(II) ion bound to closed-shell ligands. Thus, it is, to the best of our knowledge, only the second example of a stable and structurally characterized metal complex containing a reduced isolated pyridine unit. The stability is attributed to the delocalization of the unpaired electron across the two pyridine units, mediated by their interaction to the metal ion.

Gama ile Işınlanmış Klorpropamid ve Prokainamid Hidroklorür İlaç Hammaddelerinde Oluşan Serbest Radikallerin EPR Spektroskopisi ile Tanımlanması

In this study, it was aimed to determine the structural properties of free radicals formed by gamma irradiation in chlorpropamide and procainamide hydrochloride drug raw materials, which are widely used in medicine, by using electron paramagnetic resonance spectroscopy. As a result of gamma irradiation, it was determined that two different radicals were formed in both chlorpropamide and procainamide hydrochloride samples. It was suggested that –NĊH-, -NCH2ĊH2- and –NĊH-, -NĊHCH2- radicals were formed in chlorpropamide and procainamide hydrochloride samples, respectively. The simulated spectra closest to the experimental spectra recorded at room temperature of the samples studied in powder form were obtained using simulation software. The contributions of the proposed radicals to the experimental spectra were calculated. The g values of the obtained radicals and the hyperfine structure constants of the unpaired electrons were calculated.

Solvated metal complexes for balancing stability and activity of sulfur free radicals

Free radicals can improve the reaction rate, but most of them are unstable due to unpaired electrons. Simultaneously maintaining their stability and activity is challenging. Herein, taking sulfur (S) radicals as an example, we propose a strategy in which solvated metal complexes constructed by Al(acetylacetonate)3 and different solvents can stabilize high concentrations of S radicals with good activity through ion–dipole interactions. Based on this strategy, it is first demonstrated that S4·− is selectively stabilized by controlling the configurations of the solvated complexes. As a result, the reaction rate of S↔Li2S is increased by 8 times, and the energy efficiency and rate capability of the Li–S batteries are significantly improved, especially the 5-fold increase in cell capacities at a low electrolyte/sulfur ratio. This work provides an important strategy in which solvated metal complexes balance the activity and stability of free radicals to accelerate reactions and their application in various fields.

Boosting promote C2 products formation in electrochemical CO2 reduction reaction via phosphorus-enhanced proton feeding

Electrochemical CO2 reduction reaction (CO2RR) using renewable energy to produce valuable multicarbon (C2+) products is a promising approach for carbon emission reduction. In this work, we propose a new strategy to enhance the formation of hydrogen-containing intermediates using the excellent abilities of proton transportation and electronic structure modification of phosphorus (P). To realize this, an in situ electrodeposition method was proposed to prepare P-doped Cu catalysts. It was found that the electrodeposition potential significantly impacts the structure and catalytic performance of P-Cu catalysts. Specifically, the catalyst obtained at − 0.5 V vs. Ag/AgCl exhibited exceptional performance for CO2RR towards C2+ products, achieving a Faradaic efficiency (FE) of ∼ 80.2 % and a partial current density of 40.4 mA cm−2 in an H-type cell. Furthermore, the catalyst demonstrated stability for at least 12 h. Experimental and density functional theory (DFT) studies revealed that the free energy of the hydrogenated process could be significantly reduced by the excellent proton transport ability of P, and the interaction of Cu with the unpaired electrons of carbon could be improved, leading to excellent adsorption ability of Cu for the intermediates and high FE of C2+ products.

Local probe-induced structural isomerization in a one-dimensional molecular array

Synthesis of one-dimensional molecular arrays with tailored stereoisomers is challenging yet has great potential for application in molecular opto-, electronic- and magnetic-devices, where the local array structure plays a decisive role in the functional properties. Here, we demonstrate the construction and characterization of dehydroazulene isomer and diradical units in three-dimensional organometallic compounds on Ag(111) with a combination of low-temperature scanning tunneling microscopy and density functional theory calculations. Tip-induced voltage pulses firstly result in the formation of a diradical species via successive homolytic fission of two C-Br bonds in the naphthyl groups, which are subsequently transformed into chiral dehydroazulene moieties. The delicate balance of the reaction rates among the diradical and two stereoisomers, arising from an in-line configuration of tip and molecular unit, allows directional azulene-to-azulene and azulene-to-diradical local probe structural isomerization in a controlled manner. Furthermore, our theoretical calculations suggest that the diradical moiety hosts an open-shell singlet with antiferromagnetic coupling between the unpaired electrons, which can undergo an inelastic spin transition of 91 meV to the ferromagnetically coupled triplet state.

A multiferroic coupling mechanism in the polar interface region of GaN-ZnO heterojunction: A first-principle study

In this paper, the electronic structure and ferroelectric-ferromagnetic coupling properties of Y-doped and vacancy-containing GaN-ZnO heterojunctions are systematically investigated by using the generalized gradient approximation + U (GGA + U) method within the framework of density functional theory. The results reveal that in systems with vacancy defects, the magnetism is generated by the spin polarization of unpaired electrons induced by cationic vacancies, and the magnetic moment of the system is related to the number of unpaired electrons. However, in systems containing interstitial Y-doping, the s-state and d-state electrons of the Y-doped elements are coupled by orbital hybridization to form bound magnetic polarons. Compared with the system containing vacancies, the bound magnetic polaron systems have better stability, although the magnetic moments are relatively small and the total magnetic moment is limited by the concentration of bound magnetic polarons. And the modulation of different magnetic changes can be achieved in different polar interfaces by adjusting the electric polarization intensity of the bound magnetic polaron systems.

Chiral Benzene Triimide (BTI) Radical Anions for Probing the Interplay of Unpaired Electron Spin and Chirality.

Herein a series of chiral BTI radical anions bearing different chiral substituents were efficiently prepared by chemical reduction. X-ray crystallography revealed finely-tuned packing and helix assemblies of the radicals by the size of chiral substituents in crystalline state. In accordance with the crystalline-state packing, the powder ESR spectra indicate that 4 a- ⋅CoCp2 + and 4 c- ⋅CoCp2 + π-dimers exhibit thermally excited triplet states arising from strong spin-spin interactions, while discrete 4 b- ⋅CoCp2 + shows a broad doublet-state signal reflecting weak spin-spin interactions. The interplay between the unpaired electron spin and chiral substituents was studied by UV-Vis-NIR spectra, electronic circular dichroism (ECD) and TD DFT calculations. Different NIR absorptions of the radicals attributing to isolated SOMO→LUMO+1 (~889 nm) transitions were recorded. The emergence of Cotton effects (CEs) at the NIR region for 4 c- ⋅CoCp2 + radical enantiomers suggest the interplay between chirality and unpaired electron spin. The origin of the different circularly polarized light absorptions regarding SOMO derived transitions (around 880 nm) was attributed to chiral substitutes regulated electric and magnetic transition dipole moments of the unpaired electron participated transition.

Remediation of diesel-oil contaminated soils using an innovative nanobubble and electrolyzed catalytic system

Soil contamination resulting from petroleum hydrocarbons poses a significant environmental challenge. In this research, an innovative electrolyzed catalytic system was devised to produce nanobubble-enriched catalytic water, which was employed for remediating soils contaminated with diesel oil. This novel system harnessed high voltage (220 V) via direct current, utilizing titanium electrodes coated with iridium dioxide. The inclusion of iron-copper hybrid oxide catalysts between the electrodes was instrumental in enhancing the efficiency of radical generation. The study employed the electron paramagnetic resonance (EPR) technique and the Rhodamine B (RhB) method to analyze the species and concentration of the generated radicals. EPR is a versatile tool for investigating materials with unpaired electrons and is capable of quantifying reaction kinetics for transition metals. RhB can be used as a probe for hydroxyl radical concentration determination. The addition of an electrolyte (NaCl or K2SO4) could enhance the electrolytic reaction and improve radical production rate. By incorporating 20 mM of K2SO4 and utilizing 75 g of catalyst per 500 mL batch of nanobubble-contained electrolyzed catalytic water (NECW) production, with a current density of 20 mA/cm2, a highly oxidized nanobubble-infused electrolyzed catalytic water was successfully generated. This water exhibited an oxidation-reduction potential of 887 mV and contained a radical concentration of 7.6 × 10−13 M, encompassing hydroxyl, superoxide, and sulfate radicals. Furthermore, it displayed a negative zeta potential of −39.8 mV, along with nanobubbles averaging 28 nm in diameter and a nanobubble density of 3.7 × 109 particles per milliliter. The presence of nanobubbles in electrolyzed catalytic water, owing to their negative zeta potential and nano-scale attributes, imparts a repulsive force that hinders bubble aggregation and prolongs their existence. When these nanobubbles burst, the resulting radicals contribute to an augmented radical concentration, which, in turn, facilitates the oxidation of petroleum hydrocarbons. Approximately 72.4% of the total petroleum hydrocarbon in soils could be removed (dropped from 3230 mg/kg to 892 mg/kg) after five batches of NECW washing (10 min of each washing time) via the desorption and extended chemical oxidation mechanisms. The total petroleum hydrocarbons in the water phase could be removed entirely after pumping the polluted water into the electrolyzed catalytic system for immediate treatment, indicating that the electrolyzed catalytic system could oxidize the desorbed total petroleum hydrocarbon effectively. The findings demonstrate that the nanobubble-infused catalytic water generated by the innovative electrolyzed system effectively and efficiently remediates petroleum-hydrocarbon-contaminated soils and water, all while minimizing the risk of secondary pollution.

Coherences of Photoinduced Electron Spin Qubit Pair States in Photosystem I.

This publication presents the first comprehensive experimental study of electron spin coherences in photosynthetic reaction center proteins, specifically focusing on photosystem I (PSI). The ultrafast electron transfer in PSI generates spin-correlated radical pairs (SCRPs), which are entangled spin pairs formed in well-defined spin states (Bell states). Since their discovery in our group in the 1980s, SCRPs have been extensively used to enhance our understanding of structure-function relationships in photosynthetic proteins. More recently, SCRPs have been utilized as tools for quantum sensing. Electron spin decoherence poses a significant challenge in realizing practical applications of electron spin qubits, particularly the creation of quantum entanglement between multiple electron spins. This work is focused on the systematic characterization of decoherence in SCRPs of PSI. These decoherence times were measured as electron spin echo decay times, termed phase memory times (TM), at various temperatures. Decoherence was recorded on both transient SCRP states P700+A1- and thermalized states. Our study reveals that TM exhibits minimal dependence on the biological species, biochemical treatment, and paramagnetic species. The analysis indicates that nuclear spin diffusion and instantaneous diffusion mechanisms alone cannot explain the observed decoherence. As a plausible explanation we discuss the assumption that the low-temperature dynamics of methyl groups in the protein surrounding the unpaired electron spin centers is the main factor governing the loss of the spin coherence in PSI.

HTHP treatment of diamonds containing N1 centers. Neutral state of the N1 center as a limiting step in the aggregation of substitutional nitrogen into A form

The step-by-step annealing of natural plastically deformed type IaAB diamond revealed new information on the N1 center, which is two nitrogen atoms separated by one carbon in an ionized state (S = 1/2). A slight increase in the intensity of the N1 electron paramagnetic resonance (EPR) spectrum after annealing at 1000 °C (10h) was observed, and the complete disappearance was detected at a temperature of 1300 °C (4 h). This behavior of the N1 paramagnetic center was associated with the annealing of electron acceptors, and we analyzed the conditions for the formation of complex vacancy defects. The temperature of 1000 °C corresponds to the formation of three vacancy chains from single vacancies and 1300 °C corresponds to their disappearance. We experimented with electron irradiation of the crystals (energy of 3 MeV and a fluence of 1018 e/cm2) followed by annealing at 1000 °C (for 10 h) and the N1 EPR spectrum appeared back with an intensity five times higher than in the initial crystal. The next heat treatment at 1400 °C (2 h) resulted in the expected vanish of the N1 EPR spectrum. In this case, electron irradiation followed by annealing at 1000 °C led to the restoration of a very weak EPR spectrum. The presence of the “EPR-silent” N1 centers in a neutral state in plastically deformed diamond prompted us to investigate their existence in crystals that were not subjected to plastic deformation. We generated acceptor centers in different diamonds by the above method and found N1 centers in the type IaAB natural and type IaA synthetic diamonds. The results obtained can suggest that the rate-limiting step in the aggregation of two impurity nitrogen atoms into close pair is the neutral N1 defect. In the ionized state of N1, the Coulomb repulsion between the unpaired extra electrons of nitrogen is eliminated, reducing the energy barrier in the final stage of transformation into the A center.

Size matters: Computational insight into magnetic properties of extended acenes

A DFT study of a series of extended acenes comprising from 7 to 35 conjugated six-membered rings (n) predicted their polyradical character and ascertained correlation between the length and magnetic properties of these compounds. A regularity was revealed indicating that increasing the chain length by every seven rings bring into the formation of two additional paramagnetic centers, leading to the presence of ten unpaired electrons in the acene, for which n = 35. The computational results obtained allow one to expect increasing the number of unpaired electrons with a further (n > 35) expanding the acene length.

Hierarchically porous, N-defect enriched C-nanosheets boost the H2S selective oxidation to elemental sulfur

H2S selective oxidation to elemental sulfur (S8) is a typical reaction where the mass product diffusion (e.g., S8) through the catalytic bed is crucial as well as the reagents accessibility (e.g., H2S, O2) to the active sites. The NaNO3-assisted pyrolysis of polyacrylamide was applied to synthesize defect-enriched N-doped carbon nanosheets with thickness up to c.a. 2 nm, featured by fully accessible and highly interconnected pores, for boosting the H2S selective oxidation process. The PAM-0.3-700 sample has revealed an unprecedented desulfurization activity with sulfur formation rate of 1165 gsulfur kgcat.−1 h−1, other than a remarkable stability (>80 h). Experimental and theoretical studies have unveiled the critical role of edge sites containing unpaired electrons and nitrogen species with respect to the material aptitude towards O2 dissociation and HS- activation. The material in presence of a highly interconnected porous network facilitates the reactants/product diffusion especially for catalysis operated under harsh experimental conditions.

When do tripdoublet states fluoresce? A theoretical study of copper(II) porphyrin.

Open-shell molecules rarely fluoresce, due to their typically faster non-radiative relaxation rates compared to closed-shell ones. Even rarer is the fluorescence from states that have two more unpaired electrons than the open-shell ground state, since they involve excitations from closed-shell orbitals to vacant-shell orbitals, which are typically higher in energy compared to excitations from or out of open-shell orbitals. States that are dominated by the former type of excitations are known as tripdoublet states when they can be described as a triplet excitation antiferromagnetically coupled to a doublet state, and their description by unrestricted single-reference methods (e.g., U-TDDFT) is notoriously inaccurate due to large spin contamination. In this work, we applied our spin-adapted TDDFT method, X-TDDFT, and the efficient and accurate static-dynamic-static second order perturbation theory (SDSPT2), to the study of the excited states as well as their relaxation pathways of copper(II) porphyrin; previous experimental works suggested that the photoluminescence of some substituted copper(II) porphyrins originate from a tripdoublet state, formed by a triplet ligand π → π* excitation antiferromagnetically coupled with the unpaired d electron. Our results demonstrated favorable agreement between the X-TDDFT, SDSPT2 and experimental excitation energies, and revealed noticeable improvements of X-TDDFT compared to U-TDDFT, not only for vertical excitation energies but also for adiabatic energy differences. These suggest that X-TDDFT is a reliable tool for the study of tripdoublet state fluorescence. Intriguingly, we showed that the aforementioned tripdoublet state is only slightly above the lowest doublet excited state and lies only slightly higher than the lowest quartet state, which suggests that the tripdoublet of copper(II) porphyrin is long-lived enough to fluoresce due to a lack of efficient non-radiative relaxation pathways; an explanation for this unusual state ordering is given. Indeed, thermal vibration correlation function (TVCF)-based calculations of internal conversion, intersystem crossing, and radiative transition rates confirm that copper(II) porphyrin emits thermally activated delayed fluorescence (TADF) and a small amount of phosphorescence at low temperature (83K), in accordance with experiment. The present contribution is concluded by a few possible approaches of designing new molecules that fluoresce from tripdoublet states.

Characterization of iron oxides: Valence states and naturally occurring polymorphs using chemical shift of X–ray FeLβ1 line by WD–XRF

In X–ray spectroscopic studies of 3d transition metals, Kβ1,3 lines have been extensively used for the examination of chemical states. This is because Kβ1,3 lines are the second most intense X–ray lines and are more sensitive to changes in chemical state of 3d transition metals since the valence shell 3p is involved in the transition. In order to characterize iron oxides in natural iron ores, we determined the chemical shift, asymmetric index and FWHM of the third order FeKβ1,3 lines using WD–XRF technique. Unfortunately, none of these parameters exhibited good agreement with the chemical state of iron which was desired for characterization of iron oxides. Alternatively, FeL-lines were inspected because it involves the valence shell 3d electrons and moreover Fe(II) and Fe(III) have different number of unpaired electrons in the 3d shell. Hence, FeL-lines are anticipated to represent signature of different chemical states of iron. The study established a linear relationship between chemical shift of FeLβ1 line (δβ) and spin multiplicity (2S+ 1) in iron oxide ores having both Fe(II) and Fe(III) valence states. Since (2S + 1) is an intrinsic property of valence state, the study of δβ facilitated speciation of iron. The δβ also contained potential information on structural framework of iron oxides whereby it enabled characterization of various polymorphic phases of iron oxides irrespective of their crystalline/amorphous forms and structure. The δβ was found to increase with increase in Fe(III)/Fetotal ratio in the iron oxide CRMs. Hematite (α–Fe2O3) was observed to have higher δβ than maghemite (γ–Fe2O3) which is attributed to differences in their packing structure. Magnetite (Fe3O4), on the other hand, showed an anomalous behavior due to structural resemblance with maghemite, but both were characterized successfully.

Effect of unpaired electron number elements (Al, Cr, Mn) doping in Fe2O3 on ortho to para hydrogen conversion at 77 K

Para hydrogen (p-H2), as a low-energy spin isomer of hydrogen molecule, has an important significance in the storage and transportation of liquid hydrogen. The ortho hydrogen (o-H2) to p-H2 conversion catalyst accelerates the intrinsically slow o-H2 to p-H2 conversion and becomes an essential component of the hydrogen liquefaction process. In this paper, doped Fe2O3 with different hetero elements (X-FO, X = Al, Cr, Mn) are prepared by a simple co-precipitation method to explore the effect of different unpaired electron numbers in doping elements on catalytic performance. It is shown that the disorder in the internal crystal structure of X-FO caused by doping of hetero elements is the main reason for the increased performance of X-FO, as this leads directly to an increase in the internal magnetic disorder. The catalytic performance is enhanced with the increase in the number of unpaired electrons in doping elements. Mn-FO with high unpaired electron number exhibits optimal catalytic performance. When the hydrogen flow rate is 100 mL min−1, p-H2 content is 49.45 % after catalytic conversion at 77 K. In this paper, a simple method is adopted, which has advantages in terms of production process and cost, and provides experimental support for the large-scale production of catalysts.

Spin singlet pairing of bismuth in titania

The formation of electron and hole traps in semiconductors via atomistic defects is the fundamental microscopic mechanism for tuning the electronic and photonic properties of these materials. Here we find in experiments that bismuth atoms doped into anatase TiO2 as substituents can appear as paired diatomic defects. Through first-principles density functional theory calculations, we reveal that the observed bismuth pair is separated by a medium distance of 6.37 Å through a delicate balance of Pauli repulsion and effective attractive interaction. We further clarify that the effective attractive interaction is related to the exchange coupling between the two bismuth defect states, which also leads to the formation of a spin singlet electronic state of the two unpaired electrons. Our study brings up a new type of defect state in TiO2, and motivates further experimental and theoretical studies of multi-electronic states in materials.